This application claims priority to an application entitled xe2x80x9cACTIVE OPTICAL SEMICONDUCTOR HAVING A CURVED OPTICAL WAVEGUIDE,xe2x80x9d filed in the Korean Industrial Property Office on Nov. 23, 2001 and assigned Serial No. 2001-73263, the contents of which are hereby incorporated by reference.
1. Field of the Invention
The present invention relates to an optical-communication module and, more particularly to an optical device having an optical waveguide mounted on an optical communication module.
2. Description of the Related Art
An optical-waveguide device comprises an optical waveguide through which light passes and a clad surrounding the optical waveguide to allow the light to pass only through the optical waveguide. Optical-waveguide devices may include optical semiconductors to which an optical waveguide and a clad are laminated on a semiconductor substrate.
A conventional optical communication module includes active optical devices and optical waveguide devices(or optical fibers). U.S. Pat. No. 6,273,620 issued to Kato, et al., entitled xe2x80x9cSEMICONDUCTOR LIGHT EMITTING MODULExe2x80x9d, discloses an example of an optical communication module, in which the light emitting module includes a semiconductor optical amplifier with a first optical waveguide and an optical fiber grating with a second optical waveguide to which a Bragg grating is printed.
In the conventional optical communication module, the alignment between an active optical device and an optical waveguide device, which may be a passive optical semiconductor, optical fiber, or another active optical semiconductor, plays a vital role because the misalignment between them causes coupling loss between the end surfaces of the active optical device and the optical waveguide device.
FIG. 1 is a schematic partial view of the active optical device and the optical waveguide device and, in particular shows the optical loss caused by the misalignment therebetween. As shown, the optical waveguide device 120 is aligned on an optical axis 130 and includes a second optical waveguide 122 forming a passage for the light to pass therethrough and a clad 124 surrounding the second optical waveguide 122. An active optical device 110 is aligned on the optical axis 130 and includes a first optical waveguide 112 which forms a passage for light to pass therethrough, a clad 114 surrounding the first optical waveguide 112, and upper and lower electrodes (not shown) which generate and amplify the light by means of injected carriers.
In addition, the optical waveguide device 120 and the active optical device 110 contain alignment lines 118 and 126, respectively, so that they can be used to align the devices 110 and 120. For example, when the optical waveguide device 120 and the active optical device 110 are mounted on a submount (not shown), the alignment lines 118 and 126 are aligned with auxiliary lines (not shown) that are marked on the submount to correspond to the alignment lines 118 and 126, such that the optical waveguide device 120 and the active optical device 110 can be aligned correctly. This type of alignment is known as a passive alignment method.
Another alignment is known as an active alignment method. In the active alignment method, for example, the optical waveguide device 120 is fixed, then the active optical device 110 is moved while the light output from the optical waveguide device 120 is monitored, so that the location of the active optical device 110 at which the light output has a maximum value can be found.
In comparison with the passive alignment method, it can be easily seen that the active alignment method as described above requires a more time during the manufacturing stage, thus not desirable to be used in mass-production.
Referring back to FIG. 1, the light generated in the active optical device 110 is discharged through one end surface of the active optical device 110, and the discharged light is introduced into the second optical waveguide 122 through the end surface of the optical waveguide device 120. In this case, the active optical device 110 and the optical waveguide device 120 are aligned on the optical axis 130 and the end surface of the optical waveguide device 120 is in parallel with the end surface of the active optical device 110, such that the light reflected by the end surface of the optical waveguide device 120 can transmit into the first optical waveguide 112. The light transmitting back into the first optical waveguide 112 serves as noise, thereby deteriorating the output characteristics of the active optical device 110.
FIG. 2 is a schematic partial view of an active optical device and an optical waveguide device, and it shows optical loss due to a size error of the active optical device when the active optical device and an optical waveguide device are packaged according to a passive alignment method. As shown, the first and second optical axes 230 and 250 are not in parallel to each other. The optical waveguide device 240 is aligned on the second optical axis 250, and the active optical device 210 is aligned on the first optical axis 230 using the alignment lines 218 and 246.
The optical waveguide device 240 is aligned on the second optical axis 250 by means of a second alignment line 246, and includes a second optical waveguide 242 forming a passage for the light to pass through and a clad 244 surrounding the second optical waveguide 242. The active optical device 210 is aligned on the first optical axis 230 by means of a first alignment line 218 and includes a first optical waveguide 212 forming a passage for light to pass through, a clad 214 surrounding the first optical waveguide 212, and upper and lower electrodes (not shown) which generate and amplify light by means of injected carriers. The first optical waveguide 212 is tilted with respect to an end surface 215 of the active optical device 210 such that the reflected light at the end surface 215 does not couple back into the first optical waveguide 212.
In operation, the light 260 generated in the active optical device 210 is emitted through the end surface 215 of the active optical device 210. In the case of the designed active optical device 220, light 270 (shown by a broken line) emitted from the designed active optical device 220 can be incident to the second optical waveguide 242. However, when the fabricated active optical device 210 shown by solid lines has a size different from that of the designed active optical device 220 shown by broken lines, the light 260 emitted from the first optical waveguide 212 is not incident to the second optical waveguide 242, thus its coupling efficiency is deteriorated. Note that the designed active optical device 220 represents the boundary where the proposed optical device 220 supposed to line up according to the design specification, whereas the fabricated active optical device 210 represents the actual product manufactured and positioned according to the design specification. The size difference between the designed active optical device 220 and the fabricated active optical device 210 is due to fabrication error, which occurs when cleaving a processed wafer into the designed bars. The size error due to this cleaving inaccuracy is around xc2x110 xcexcm when working with InP or GaAs compound semiconductors. As a result, the light emitted from the end surface 215 of the active optical device 210 misses the second optical axis 250.
The present invention has been made to solve the above-mentioned problems occurring in the prior art and provides additional advantages, by providing an optical device that can prevent the deterioration of the optical coupling efficiency due to the size error in the optical device when the optical device and an optical waveguide device are packaged according to a passive alignment method.
Accordingly, there is provided an optical communication module comprising: an optical device including a first optical waveguide through which light passes; and, an optical waveguide device including a second optical waveguide, the second optical waveguide having an input end surface through which the light emitted from an output end of the first optical waveguide that is incident into the second optical waveguide, wherein the output end of the first optical waveguide includes a first unit vector which represents a direction in which light passing a predetermined first point on the output end proceeds, and the first unit vector forms a curve satisfying an equation, n1{right arrow over (L)}1xc3x97{right arrow over (A)}=n2{right arrow over (L)}2xc3x97{right arrow over (A)}, in which n1, {right arrow over (L)}1, {right arrow over (A)}, n2, and {right arrow over (L)}2 signify a refractive index of the first optical waveguide 312, the first unit vector, a normal vector of the first end surface, a refractive index of a medium in contact with the first end surface, and the second unit vector oriented toward the origin from the first point C.